Ferecrystals are a new family of compounds first synthesized in 2007 by the group of D. Johnson at the University of Oregon. These materials consist of inter-growths of dichalcogenide and chalcogenide ... [more ▼]

Ferecrystals are a new family of compounds first synthesized in 2007 by the group of D. Johnson at the University of Oregon. These materials consist of inter-growths of dichalcogenide and chalcogenide layers, and can be written as [(M X)_{1+δ} ]_m [T X_2 ]_n where M = Sn, Pb, Sb, Ni and some rare earths; T = Ti, V, Cr, Nb and Ta; X= S and Se. The integers m and n denote the numbers of consecutive formula unit layers in the different components of the inter-growth. The δ parameter reflects the difference of the in-plane cell constants between components of the inter-growth. This family of nanostructured materials shows promising properties for thermoelectric devices. The compounds studied here are [(SnSe)_1.29 ]_{234} [M oSe_2 ]_1 . We performed structural characterisation and examined the transfer of charge at the interface between the two materials. We show that there is a depletion of charge at the interface between the two compo- nents of the heterostructures and that structural distortions of the SnSe layers in the supercell are similar to those observed in slab calculations. [less ▲]

By means of first-principles calculations, various properties of SrRuO3 are investigated, focusing on its lattice dynamical properties. Despite having a Goldschmidt tolerance factor very close to 1, the ... [more ▼]

By means of first-principles calculations, various properties of SrRuO3 are investigated, focusing on its lattice dynamical properties. Despite having a Goldschmidt tolerance factor very close to 1, the phonon dispersion curves of the high-temperature cubic phase of SrRuO3 show strong antiferrodistortive instabilities. The energetics of metastable phases with different tilt patterns are discussed, concluding that the coupling of oxygen rotation modes with anti-polar Sr motion plays a key role in stabilizing the Pnma phase with respect to alternative rotation patterns. Our systematic analysis confirms previous expectations and contributes to rationalizing better why many ABO3 perovskites, including metallic compounds, exhibit an orthorhombic ground state. The zone-center phonon modes of the Pnma phase have been computed, from which we propose partial reassignment of available experimental data. The full dispersion curves have also been obtained, constituting benchmark results for the interpretation of future measurements and providing access to thermodynamical properties. [less ▲]

We report on the crystal structure and electronic bands of LaAu2 and CeAu2 surface intermetallic compounds grown by high-temperature deposition on Au(111). By scanning-tunneling microscopy we study the ... [more ▼]

We report on the crystal structure and electronic bands of LaAu2 and CeAu2 surface intermetallic compounds grown by high-temperature deposition on Au(111). By scanning-tunneling microscopy we study the formation of different alloy phases as a function of growth temperature and lanthanide coverage. We determine the specific growth conditions to achieve monolayers and bilayers of LaAu2 and CeAu2 with high crystalline quality. Due to lattice mismatch with the underlying Au substrate, both LaAu2 and CeAu2 exhibit long-range moire ́ patterns, which can serve as templates for further nanostructure growth. By angle-resolved photoemission we map the two-dimensional band structure of these surface alloys, discussing the nature of the different spectral features in the light of first-principles calculations. [less ▲]

The spin-dependent coupling between electrons and phonons in ferromagnetic Fe and Co is calculated from first principles in a collinear-spin formalism. The added spin polarization is fundamental for the ... [more ▼]

The spin-dependent coupling between electrons and phonons in ferromagnetic Fe and Co is calculated from first principles in a collinear-spin formalism. The added spin polarization is fundamental for the correct representation of the phonons, but also to obtain good transport properties, and permits the decomposition (e.g. of the resistivity) into the contributions of majority and minority spin. In Fe the minority spin coupling is only about 50\% more important, but in Co the coupling between phonons and minority spin electrons is an order of magnitude larger than majority, and both are strongly anisotropic. [less ▲]

We analyze how functionality could be obtained within single-molecule devices by using a combination of non-equilibrium Green's functions and ab initio calculations to study the inelastic transport ... [more ▼]

We analyze how functionality could be obtained within single-molecule devices by using a combination of non-equilibrium Green's functions and ab initio calculations to study the inelastic transport properties of single-molecule junctions. First, we apply a full non-equilibrium Green's function technique to a model system with electron-vibration coupling. We show that the features in the inelastic electron tunneling spectra (IETS) of the molecular junctions are virtually independent of the nature of the molecule-lead contacts. Since the contacts are not easily reproducible from one device to another, this is a very useful property. The IETS signal is much more robust versus modifications at the contacts and hence can be used to build functional nanodevices. Second, we consider a realistic model of a organic conjugated molecule. We use ab initio calculations to study how the vibronic properties of the molecule can be controlled by an external electric field which acts as a gate voltage. The control, through the gate voltage, of the vibron frequencies and (more importantly) of the electron-vibron coupling enables the construction of functionality: nonlinear amplification and/or switching is obtained from the IETS signal within a single-molecule device. [less ▲]